The excess urine Ca excretion in patients with idiopathic hypercalciuria (IH) contributes to the formation of calcium kidney stones, and increased intestinal Ca absorption and enhanced bone resorption are the sources of the excess urine Ca. The hypothesis that increased Ca absorption and bone resorption are due to increased target tissue vitamin D receptor content will be tested in patients and non-stone forming controls. They will undergo six day mineral balance, vitamin D receptor content measurements in intestinal mucosal biopsies and in peripheral blood monocytes, and regulation of parathyroid hormone and calcitrol synthesis.